A steam turbine is arranged on an ordinary concrete foundation. FIG. 1 is a side cross-sectional view showing diagrammatically a steam turbine of a form in which a turbine rotor is supported by bearings that are arranged on conical portions of the casing.
The steam turbine 10 shown in FIG. 1 is a low pressure steam turbine, with a steam inlet section arranged in the middle and steam exhaust sections arranged at both sides, and comprises: foundations 14 that are formed by concrete sections 16; a casing 13 that is supported by these foundations 14; a turbine rotor 12 that is inserted in this casing 13; and bearings 15 whereby this turbine rotor 12 is freely rotatably supported at both sides and that are arranged on conical portions 13C of the lower part of the casing 13, by means of bearing support sections 15S.
A base plate 24 is arranged at the top of the concrete sections 16 of the foundations 14.
Also, moving blades 11 are provided on the turbine rotor 12, so that a turbine stage is constituted between these and stator blades (stator vanes), not shown, that are fixed to a stationary section on the side of the casing 13.
In modern steam turbines 10, the turbine rotor 12 is of large size due to the need for large capacity and high output, so, in a configuration in which the turbine rotor 12 is supported arranged on bearings 15 on conical portions 13C of the casing 13 as in FIG. 1, over the years, the casing 13 itself is deformed by the weight of the turbine rotor 12, leading to problems such as that stationary parts and rotary parts may come into contact, or vibration of the turbine rotor 12 due to difficulty in maintaining rigidity of the conical portions 13C.
In order to solve these problems, steam turbines 10 have been developed in which, as in FIG. 2, the bearings 15 are shifted to the top of the concrete sections 16 of the foundations 14, further towards the outside than the conical portions 13C, and in which the turbine rotor 12 is supported with the bearings 15 fixed on the concrete sections 16 of the foundations 14 with interposition of a base plate 24.
However, with the steam turbine 10 shown in FIG. 2, the distance between the bearings 15, 15 becomes large, since the bearings 15 are arranged outside the conical portions 13C of the casing 13. In general, it is known that increasing the distance between the bearings 15, 15 makes the turbine rotor 12 more liable to vibrate. While vibration of the turbine rotor 12 can be effectively suppressed by reducing the distance between the bearings 15, 15, if the axial length dimension of the casing 13 becomes small, the turbine performance is severely impaired, so that is not possible to reduce the distance between the foundations 14, 14 to less than a certain distance.
Furthermore, in order to improve these problems of the steam turbine 10 of the form shown in FIG. 2, inventions have also been proposed in which the distance between the bearings 15, 15 is reduced, without altering the distance between the foundations 14, 14, by embedding a plurality of rectangular plate-shaped reinforcing members, arranged next to each other in the same direction, in the perpendicular direction with respect to the top of the concrete sections 16 of the foundations 14, with their ends extending towards the turbine blades 11, the bearings 15 being supported on these extended portions. Examples are Laid-open Japanese Patent Application Number Tokkai S52-57412 (hereinafter referred to as Patent Reference 1) and, likewise, Laid-open Japanese Patent Application Number Tokkai 2003-278504 (hereinafter referred to as Patent Reference 2).